This invention relates to a wholly aromatic polyester having excellent formability for giving various formed products having excellent mechanical properties and thermal properties.
Demands for higher performances of organic polymeric materials have been increasing in the industry, and strongly desired are various formed products such as fiber, film, injection molded product, etc. having superior mechanical properties such as strength and elastic modulus and thermal properties such as heat resistance.
As a polymeric material meeting the above demands, a polyester which forms an optically anisotropic melt phase, that is, so-called thermotropic liquid crystal polyester has drawn attention, and have so far been proposed thermotropic liquid crystal polyesters of various structures, of which several have been industrially produced.
Such polymers can form a product having a highly oriented molecular structure upon melt processing. Such product has been found to exhibit an excellent mechanical properties. Further it is well known that various formed products obtained from wholly aromatic thermotropic liquid crystal polyester consisting only of aromatic rings have markedly good thermal resistance.
As described above, wholly aromatic thermotropic liquid crystal polyester is excellent as a high performance material, and particularly a wholly aromatic thermotropic liquid crystal polyester derived from p-hydroxybenzoic acid, terephthalic acid and 4,4'-dihydroxydiphenyl has been under a commercial name of Xydar industrially produced. However, since the wholly aromatic thermotropic polyester derived from p-hydroxybenzoic acid, terephthalic acid and 4,4'-dihydroxydiphenyl has a markedly high temperature of transition to liquid crystal phase, that is, melting point of more than 400.degree. C., the meld forming process requires a high temperature of more than 400.degree. C., thus making it difficult to form with a conventional molding machine, requiring a special forming machine.
For the purpose of lowering the melting point to facilitate the melt processing, a method which comprises copolymerizing a small amount of 2-hydroxy-6-naththoic acid ( U.S. Pat. Nos. 4,473,682 and 4,522,974 ) has been proposed.